A valve end, or apex, having the shape of a head, or the shape of a rounded knob.
Other terms for valve ends include subcapitate (less strongly capitate), rostrate, and subrostrate (less strongly rostrate). Subcapitate and subrostrate are quite similar and many taxa may be described as having subcapitate to subrostrate valve ends.
In general, capitate and subcapitate ends are more expanded than the most narrow point on the valve, while rostrate and subrostrate ends are not more expanded than the most narrow point.
Barber, H.G. and Hayworth, E.Y. (1981). Guide to the Morphology of the Diatom Frustule. Freshwater Biological Association, 112 pp.